The use of riser sleeves is well known in the prior art. Riser sleeves are used as a conduit within which molten metal is accumulated before the molten metal ultimately flows from the riser sleeve into a preformed cavity within a mold. Riser sleeves are manufactured from heat insulating materials to prevent the molten metal from solidifying within the riser sleeve before it passes to the preformed cavity. Typically, riser sleeves are manufactured from heat insulating refractory materials, including man made fibers. Riser sleeves can include fuels such as aluminum or silicon which are used to produce their respective heat insulating oxides during an exothermic reaction within the riser sleeve. Riser sleeves are produced to have low densities and high porosities to provide additional good heat insulating properties.
There are two major types of riser sleeves in the prior art: open top riser sleeves and blind riser sleeves. Blind riser sleeves comprise a hollow dome shaped riser sleeve, whereas open top riser sleeves are generally annular shaped. Blind riser sleeves are more expensive to manufacture and are only used in special applications. Open top riser sleeves allow the casting operator to see the progress of the cast by visualizing the level of the molten metal in the riser sleeve. Because of their prevalence, for purposes of this specification and the claims, the term riser sleeve only refers to open top riser sleeves.
Patterns are used to create a mold cavity conforming to the casting configuration. Riser plugs or riser location plugs, hereinafter referred to as plugs, are used to create the riser passage itself and to locate the riser sleeve in a desired position on the casting. In operation the riser sleeves hold a reservoir of liquid metal in fluid communication with the mold cavity. The plugs are positioned on the casting in a location which provide a liquid metal to compensate for the volumetric change which takes place in the cooling metal within the mold cavity.
During the formation of the mold, the plug is positioned adjacent the selected pattern and the prior art riser sleeves are placed on the plug. The plug is made to be slightly smaller than the nominal interior diameter of the riser sleeve. However plugs are typically not symmetrical in shape and gaps between the plug and the interior surface of the riser sleeve are common.
There are two types of molding sand typically used in the preparation of a mold, i.e. "green" sand and "nobake" sand. Green sand is composed of sand, clays, water and other additives. No-bake sand is composed of sand and bonding agents such as resins, catalysts and other additives to create a chemically bonded self hardening molding sand. Both of these molding sands are placed about the exterior of the pattern assembly by means of hand ramming, machine jolting and squeezing, high pressure squeezing, sand slinging etc. to form the mold. When the molding sand is positioned in this way, it often accumulates in the interstitial space formed by the external surface of the plug and the internal surface of the riser sleeve. In the case of the self hardening no-bake sand, when the molding sand hardens it is difficult to remove the plug from the riser sleeve without hammering the plug from the sleeve or otherwise coercing it. When such coercive forces are used on the plug, or pattern assembly the plug and pattern may become damaged requiring repair. Also the vibration from the coercive forces causes the riser sleeve to become loosened from the surrounding molding medium causing it to shift during pouring, producing an undesired lump or fin on the casting which must be removed by grinding or other removal method.
This prior art riser sleeve can also produce quality control problems. The molding sand which accumulates in the interstitial space between the riser sleeve and the plug must be removed. The accumulated molding sand is most often a thin layer of sand left adhered to the internal wall of the riser sleeve after the plug is removed. The frequency which this layer of sand is formed is such that a position on the metal casting assembly line is dedicated to the task of removing it. This sand layer is removed with the aid of implements such as a molders trowel or file. The removal is necessary to prevent the sand from later falling into the mold cavity during movement of mold or while the mold is filled with molten metal. Any sand which so enters the mold cavity creates unwanted inclusions and unacceptable metallurgical imperfections which must be removed from the casting after it has cooled. This removal process is very time consuming and costly.
Thus, there exists a need in the prior art for a sealing apparatus to prevent molding sand from entering the passage within the riser sleeve.